U.S. patent number 6,494,955 [Application Number 09/596,854] was granted by the patent office on 2002-12-17 for ceramic substrate support.
This patent grant is currently assigned to Applied Materials, Inc.. Invention is credited to Anzhong Chang, Lawrence Chung-Lai Lei, Anh N. Nguyen, Ron Rose, Hongbee Teoh, Sal Umotoy, Xiaoxiong Yuan.
United States Patent |
6,494,955 |
Lei , et al. |
December 17, 2002 |
Ceramic substrate support
Abstract
A substrate support assembly for supporting a substrate during
processing is provided. In one embodiment, a support assembly
includes a top ceramic plate having a first side, a bottom ceramic
plate having a first side and an embedded electrode, the first side
of the bottom plate fused to the first side of the top plate
defining a channel therebetween. In another embodiment, a support
assembly includes a first plate having a first side and second
side. A ring is disposed on the first side. A stepped surface is
formed on the first side radially inward of the ring. A second
plate is connected to the second side of the first plate.
Inventors: |
Lei; Lawrence Chung-Lai
(Milpitas, CA), Umotoy; Sal (Antioch, CA), Yuan;
Xiaoxiong (Cupertino, CA), Chang; Anzhong (San Jose,
CA), Teoh; Hongbee (Saratoga, CA), Nguyen; Anh N.
(Milpitas, CA), Rose; Ron (Los Gatos, CA) |
Assignee: |
Applied Materials, Inc. (Santa
Clara, CA)
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Family
ID: |
24388994 |
Appl.
No.: |
09/596,854 |
Filed: |
June 19, 2000 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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504288 |
Feb 15, 2000 |
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Current U.S.
Class: |
118/715; 118/724;
118/725; 118/728; 156/345.51; 156/345.52 |
Current CPC
Class: |
C23C
16/4586 (20130101); C23C 16/4581 (20130101); H01L
21/67017 (20130101); H01L 21/68735 (20130101); C23C
16/45521 (20130101); H01L 21/6875 (20130101); H01L
21/68721 (20130101); H01L 21/68785 (20130101); H01L
21/68792 (20130101) |
Current International
Class: |
H01L
21/687 (20060101); H01L 21/67 (20060101); H01L
021/205 (); H01L 021/360 (); C23C 016/00 () |
Field of
Search: |
;118/725,728,729,730,500
;156/345 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0 668 607 |
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Aug 1995 |
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EP |
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99/67440 |
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Dec 1999 |
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WO |
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Other References
Yodovsky et al. "Fastening Device for Purge Ring" U.S. patent
application No. 09/504,288 filed Feb. 15, 2000. .
European Search Report from EP 01 30 5217, Dated Sep. 12, 2001.
.
Search Report for EP No. 01301314.9, dated Jun. 13, 2001. .
Shamouilian, et al., "Multi-Layer Ceramic Electrostatic Chuck with
Integrated Channel", U.S. patent application, Ser. No. 09/149,807,
filed Sep. 8, 1998. .
Yudovsky, et al., "Self Aligning Non Contact Shadow Ring Process
Kit", U.S. patent application, Ser. No. 09/459,313, filed Dec. 10,
1999..
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Primary Examiner: Mills; Gregory
Assistant Examiner: Kackar; Ram N
Attorney, Agent or Firm: Moser, Patterson, and Sheridan,
LLP
Parent Case Text
This application is a continuation-in-part of co-pending U.S.
patent application Ser. No. 09/504,288, filed Feb. 15, 2000,
entitled "Fastening Device for a Purge Ring", which is hereby
incorporated by reference in its entirety.
Claims
What is claimed is:
1. A support assembly for supporting a workpiece comprising: a top
ceramic plate having a first side and an outer diameter; a bottom
plate having a first side and an embedded electrode, the first side
of the bottom plate connected to the first side of the top ceramic
plate, the bottom plate extending beyond the outer diameter of the
top ceramic plate; and a channel defined between the first side of
the top ceramic plate and the first side of the bottom plate, the
channel adapted to flow a fluid outward of the outer diameter of
the top ceramic plate.
2. The support assembly of claim 1, wherein the channel is at least
partially defined in the top ceramic plate.
3. The support assembly of claim 1, wherein the channel is at least
partially defined in the bottom plate.
4. The support assembly of claim 1, wherein the bottom plate
further comprises: a hole disposed through the bottom plate in
communication with the channel.
5. The support assembly of claim 4, wherein the channel further
comprises a plurality of passages, each passage coupling the
central origin with an outlet.
6. The support assembly of claim 5, wherein the passages comprises:
one or more shorter passages; and one or more longer passages
having a cross section greater than the shorter passages.
7. The support assembly of claim 5, wherein the channel and outlets
are disposed in the bottom plate.
8. The support assembly of claim 5, wherein at least one of the
outlets further comprises a flow restrictor disposed therein.
9. The support assembly of claim 5, wherein the channel further
comprises: a primary channel having a mid-point coinciding with the
central origin; and a first secondary channel, a second secondary
channel and a third secondary channel branching from each end of
the primary channel, the first secondary channel, the second
secondary channel and the third secondary channel each coupling the
primary channel to the outlets.
10. The support assembly of claim 1, wherein the top ceramic plate
further comprises: a second surface adapted to support the
substrate; and a vacuum port disposed at least partially in the
second surface.
11. The support assembly of claim 1, wherein the top ceramic plate
further comprises: a second surface adapted to support the
substrate; a vacuum port disposed through the top ceramic plate;
and an enlarged portion of the vacuum port disposed at least
partially In the second surface.
12. The support assembly of claim 1, wherein the top ceramic plate
further comprises; a stepped surface disposed on a second side of
the top ceramic plate, the second side disposed opposite the first
side.
13. The support assembly of claim 12, wherein the stepped surface
further comprises: a center portion, an intermediate portion and an
outer portion, wherein a center portion extends farthest below the
second side of the top ceramic plate.
14. The support assembly of claim 12, wherein the stepped surface
further comprises: an outer portion; an intermediate portion that
extends 0.001 inches below the outer portion; and a center portion
that extends 0.001 inches below the intermediate portion.
15. The support assembly of claim 12, wherein the stepped surface
further comprises: a plurality of posts extending therefrom.
16. The support assembly of claim 1, wherein the bottom plate
further comprise aluminum nitride.
17. The support assembly of claim 1 further comprising: a ceramic
stem connected to the bottom plate.
18. The support assembly of claim 17, where the stem further
comprises: a central, axial passage; a first gas passage disposed
adjacent to the central passage; and a second gas passage disposed
adjacent to the central passage.
19. The support assembly of claim 17, where the stem further
comprises: a central, axial passage; a first gas passage disposed
adjacent to the central passage; and a second gas passage disposed
adjacent to the first gas passage, the second gas passage and the
first gas passage on opposite sides of the central passage.
20. The support assembly of claim 1 further comprising; a ceramic
stem having a first end and a second end; the first end fused to
the bottom plate; and a heat transfer block disposed coupled to the
second end.
21. The support assembly of claim 20, wherein the heat transfer
block further comprises: a first surface having a plurality of
projections; and a seal disposed between the projections.
22. The support assembly of claim 21 further comprising: an
insulator disposed between the heat transfer block and the
stem.
23. The support assembly of claim 20, wherein the heat transfer
block further comprises: a plurality of heat transfer passages
disposed therein.
24. The support assembly of claim 1, wherein the top ceramic plate
further comprises: a second side disposed opposite the first side;
a center portion, an intermediate portion, and an outer portion
formed in the second side and defining a stepped surface adapted to
support the substrate, wherein a center portion extends farthest
below the second side of the top ceramic plate; a plurality of
posts extending from the stepped surface; a vacuum port disposed
through the top ceramic plate; and an enlarged portion of the
vacuum port disposed in the center portion.
25. The support assembly of claim 1 further comprising: a ring
disposed on the second plate; and a plenum defined between the ring
and the first plate, the plenum in communication with the
channels.
26. A support assembly for supporting a workpiece comprising: a top
plate having a first side and second side; a ring disposed on the
first side; a stepped surface formed on the first side radially
inwards of the ring, the stepped surface having a center portion,
an intermediate portion and an outer portion, wherein a center
portion extends farthest below the first side of the top plate; and
a bottom plate connected to the second side of the top plate.
27. The support assembly of claim 26 further comprising: a channel
defined between the second side of the top plate and the bottom
plate.
28. The support assembly of claim 26 further comprising: a heater
embedded in the bottom plate.
29. The support assembly of claim 26 further comprising: a
plurality of posts extending from the stepped surface; each post
having a distal end substantially coplanar with the ring.
30. The support assembly of claim 26, wherein the stepped surface
further comprises: an outer portion; an intermediate portion that
extends 0.001 inches below the outer portion; and a center portion
that extends 0.001 inches below the intermediate portion.
31. A support assembly for supporting a workpiece comprising: a top
ceramic plate having a first side; a bottom ceramic plate having a
first side and an embedded electrode, the first side of the bottom
plate fused to the first side of the top plate; a channel defined
between the first side of the top plate and the first side of the
bottom plate, the channel extending to a perimeter of the top
plate; a ceramic stem fused to the bottom plate having a center
passage, a purge gas passage and a vacuum passage, the purge gas
passage coupled to the channel; and a cooling block coupled to the
stem.
32. A semiconductor process chamber comprising: a chamber having
sidewalls and a lid defining a process volume; a top ceramic plate
having a first side disposed in the process volume; a bottom
ceramic plate having a first side and an embedded electrode, the
first side of the bottom ceramic plate fused to the first side of
the top ceramic plate; a channel defined between the first side of
the top ceramic plate and the first side of the bottom ceramic
plate, the channel extending to a perimeter of the top plate; a
ceramic stem fused to the bottom ceramic plate having a center
passage, a purge gas passage and a vacuum passage; a cooling block
coupled to the stem; and a shadow ring disposed on the bottom
ceramic plate and defining an annular plenum with the top ceramic
plate, the plenum coupled to the purge gas passage by the
channel.
33. The semiconductor process chamber of claim 32, wherein the
chamber is a chemical vapor deposition chamber.
34. A support assembly for supporting a workpiece comprising: a top
ceramic plate having a first side; a bottom ceramic plate having a
first side connected to the first side of the top ceramic plate,
the bottom ceramic plate having a diameter greater than the top
ceramic plate; and a channel defined between the first side of the
top ceramic plate and the first side of the bottom ceramic plate,
the channel extending to a perimeter of the top ceramic plate.
35. The support assembly of claim 34, wherein the bottom ceramic
plate further comprises: an electrode embedded therein.
Description
BACKGROUND OF THE DISCLOSURE
1. Field of Invention
The invention relates generally to an apparatus for supporting a
substrate in a semiconductor processing chamber.
2. Background of the Invention
Integrated circuits have evolved into complex devices that can
include millions of transistors, capacitors and resistors on a
single chip. The evolution of chip designs continually requires
faster circuitry and greater circuit density that demand
increasingly precise fabrication processes. One fabrication process
frequently used is chemical vapor deposition (CVD).
Chemical vapor deposition is generally employed to deposit a thin
film on a substrate or semiconductor wafer. Chemical vapor
deposition is generally accomplished by introducing a precursor gas
in to a vacuum chamber. The precursor gas is typically directed
through a showerhead situated near the top of the chamber. The
precursor gas reacts to form a layer of material on a surface of
the substrate that is positioned on a heated substrate support.
Purge gas is routed through holes in the support to the edge of the
substrate to prevent deposition at the substrate's edge that may
cause the substrate to adhere to the support. Volatile by-products
produced during the reaction are pumped from the chamber through an
exhaust system.
One material frequently formed on substrates using a chemical vapor
deposition process is tungsten. A precursor gas that may be used to
form tungsten generally includes tungsten hexafluoride (WF.sub.6)
and silane. As the silane and tungsten hexafluoride mix, some
"stray" tungsten (i.e., tungsten that does not deposit on the
substrate) deposits on the showerhead and other chamber components.
The stray tungsten film builds on the showerhead and may become a
source of contamination in the chamber. Eventually, the stray
tungsten may clog the holes in the showerhead that facilitate the
passage of the precursor gas therethrough necessitating the
showerhead be removed and cleaned or replaced.
To extend the interval in time between the routine maintenance of
the showerhead, fluorine based chemistries are generally used to
clean (i.e., etch away) the stray tungsten film. However, the use
of fluorine, while advantageous for removing tungsten, reacts to
form a layer of aluminum fluoride on the heated support that is
commonly made of aluminum. The aluminum fluoride layer has a
generally rough surface topography. The rough surface creates a
leak path that impairs the vacuum used to chuck or hold the
substrate to the heated support. Additionally, the aluminum
fluoride layer is a potential source of particulate
contamination.
Substrate supports fabricated from ceramic materials provide an
improvement over aluminum supports due to ceramic's resistance to
fluorine. However, ceramic supports are difficult to fabricate. For
example, the holes in ceramic support used to provide purge gas to
the perimeter of the support are typically drilled from the
perimeter of the support to a depth generally equal to the radius
of the support. Drilling such a deep hole in ceramic is difficult.
The tools used to make these holes are frequently broken during the
fabrication (e.g., drilling) process. Broken tools disposed within
the support must be removed or the support must be scrapped. These
fabrication difficulties result in costly supports and an
undesirable high scrap rate.
Therefore, there is a need in the art for an improved heated
support for chemical vapor deposition processes.
SUMMARY OF INVENTION
One aspect of the present invention generally provides a substrate
support assembly for supporting a substrate during processing. In
one embodiment, a support assembly comprising a top ceramic plate
having a first side, a bottom ceramic plate having a first side and
an embedded electrode, the first side of the bottom plate fused to
the first side of the top plate defining a channel therebetween is
provided.
In another embodiment, a support assembly includes a first plate
having a first side and second side. A ring is disposed on the
first side. A stepped surface is formed on the first side radially
inward of the ring. A second plate is connected to the second side
of the first plate.
BRIEF DESCRIPTION OF DRAWINGS
The teachings of the present invention can be readily understood by
considering the following detailed description in conjunction with
the accompanying drawings, in which:
FIG. 1 depicts a schematic sectional view of one embodiment of a
processing chamber of the present invention;
FIG. 2A depicts a partial sectional view of a heater assembly;
FIG. 2B depicts a partial plan view of the heater assembly;
FIG. 3A depicts one embodiment of a surface of an upper plate;
FIG. 3B depicts another embodiment of a surface of an upper
plate;
FIG. 3C depicts another embodiment of a surface of an upper
plate;
FIG. 4 depicts a cross section view of a stem; and
FIG. 5 depicts an exploded view of a second end of the stem.
To facilitate understanding, identical reference numerals have been
used, where possible, to designate identical elements that are
common to the figures.
DETAIL DESCRIPTION OF INVENTION
The present invention generally provides a processing system and
heated substrate support that are advantageous for the deposition
of tungsten films. The invention is illustratively described below
as a chemical vapor deposition system, such as a WxZ.TM. metal
chemical vapor deposition (MCVD) system, available from Applied
Materials, Inc., of Santa Clara, Calif. However, it should be
understood that the invention has utility when depositing other
films and in other system configurations such as physical vapor
deposition systems, chemical vapor deposition systems and any other
system in which supporting a substrate on a ceramic support is
desired.
FIG. 1 is a cross sectional view of one embodiment of a chemical
vapor deposition system 100. The system generally includes a
chamber 102 coupled to a gas source 104. The chamber 102 has walls
106, a bottom 108 and a lid 110 that define a process volume 112.
The walls 106 and bottom 108 are typically fabricated from a
unitary block of aluminum. The chamber 100 contains a pumping ring
114 that couples the process volume 112 to an exhaust port 116
(that includes various pumping components not shown).
The lid 110 is supported by the walls 106 and can be removed to
service the chamber 102. The lid 110 is generally comprised of
aluminum and may additionally contain heat transfer fluid channels
for regulating the temperature of the lid 110 by flowing heat
transfer fluid therethrough.
A showerhead 118 is coupled to an interior side 120 of the lid 110.
The showerhead 118 is typically fabricated from aluminum. The
showerhead generally includes a perimeter mounting ring 122 that
surrounds a "dish-shaped" center section 124. The mounting ring 122
includes a plurality of mounting holes 126 passing therethrough,
each accepting a vented mounting screw 128 that threads into a
mating hole 130 in the lid 110. The center section 124 includes a
perforated area 132.
A mixing block 134 is disposed in the lid 110. The mixing block 134
is coupled to the gas source 104 such that process and other gases
may be introduced to the process volume 112 by passing through the
mixing block 134 and showerhead 118. A blocker plate 136 disposed
between the showerhead 118 and the mixing block 134 increases the
uniform distribution of gases passing through the showerhead 118
into the chamber 102.
A support assembly 138 is disposed beneath the showerhead 118. The
support assembly 138 supports a substrate 140 during processing.
The support assembly 138 is typically accessed by the substrate 140
through a port (not shown) in walls 106. Generally, the support
assembly 138 is coupled to a lift system 144 that moves the support
assembly 138 between an elevated position as shown and a lowered
position. Bellows 146 provides a vacuum seal between the process
volume 112 and the atmosphere outside the chamber 102 while
facilitating the movement of the support assembly 138. Lift pins
and the associated mechanisms have been omitted for clarity.
FIG. 2A depicts the support assembly 138 in cross section. The
scale of FIG. 2A has been exaggerated to clearly depict the
features of the support assembly 138. The support assembly 138
generally includes a substrate support 202 and a stem 204. The
substrate support 202 is comprised of a first (upper) plate 208 and
a second (lower) plate 210. The upper plate 208 supports the
substrate 140 during processing. The lower plate 210 generally has
a first side 212 that is connected to the upper plate 208 and a
second side 214 that is connected to the stem 204. The upper plate
208 and lower plate 210 are typically fused together, for example,
by clamping the plates 208 and 210 together at an elevated
temperature for a period of time, typically without a bonding
agent. Alternatively, the plates may be coupled by sintering,
adhesives, mechanical means (i.e., fasteners), and the like.
The upper plate 208 is fabricated from ceramic, such as aluminum
nitride. Preferably, about 95 percent pure aluminum nitride is used
to enhance the thermal conductivity of the upper plate 208. The
upper plate 208 includes a first or support surface 216 and a
second surface 232A. The support surface 216 has a seal ring 218
that projects from the perimeter of the support surface 216. The
seal ring 218 supports the substrate 140 at its perimeter and
provides a seal therebetween to facilitate vacuum chucking of the
substrate. The support surface 216 includes stepped surface 220
disposed radially inside the seal ring 218. In one embodiment, the
stepped surface 220 includes a center portion 222, an intermediate
portion 224 and an outer portion 226. The center portion 222 is
orientated parallel to a plane defined by the seal ring 218. The
intermediate portion 224 is orientated parallel to the center
portion 222. The intermediate portion 224 is positioned between the
center portion 222 and the seal ring 218. The outer portion 226 is
orientated parallel to the center portion 222. The outer portion
226 is positioned between the intermediate portion 224 and the seal
ring 218. Generally, 0.001 inches separate the planes defined by
the portions 222, 224 and 226.
A plurality of posts 228A, 228B and 228C are disposed on the
stepped surface 220 (e.g., portions 222, 224 and 226). The posts
228A, 228B and 228C are typically integrally formed in the upper
plate 208. The posts 228A are positioned in the center portion 222.
The posts 228B are positioned in the intermediate portion 224 and
the posts 228C are positioned in the outer portion 226. The posts
228A are slightly longer than the posts 228B and 228C. The posts
228B are slightly longer than the posts 228C. Each of the posts
228A, 228B and 228C includes a distal end 230 that lie in a common
plane. The plane defined by the distal ends 230 may be
substantially co-planar to the plane of the seal ring 218 such that
the substrate is supported on the distal ends 230 of the posts
228A, 228B and 228C during processing without damaging the
substrate by excessive flexing (i.e., bowing the substrate across
the seal ring and posts).
The stepped surface 220 provides a larger gap between the substrate
and the center portion 222 to compensate for the tendency of the
substrate to transfer heat to its center. Thus, the variable gap
created between the substrate and the stepped surface 220 promotes
better chucking effect for substrate 140 since size of caps and
plural posts can be designed to attain better temperature
uniformity. For example, the temperature uniformity across the
support assembly 138 can be within about 3 degrees Celsius.
A vacuum port 250 is disposed through the upper plate 208. The
vacuum port 250 has a varied cross section that includes an
expanded portion 252 on the support surface 216 that has a
generally larger cross sectional area relative the other portions
of the vacuum port 250. In one embodiment, the expanded portion 252
comprises a slot having a full radius at each end. The expanded
portion 252 serves to decrease the pressure drop at the interface
of the vacuum port 250 and support surface 216 during the
application of the vacuum. This enhances temperature uniformity,
and consequently deposition uniformity on the substrate 140. One
skilled in the art will readily identify that the expanded portion
252 may be configured in other geometries to accomplish the
pressure reduction at the surface 216 disclosed herein.
A channel 290 is formed between the upper and lower plates 208 and
210. Generally, the channel 290 provides a passage for purge gas
through the substrate support 202 to a plenum 266 defined between a
shadow ring 258 and the support 202. The purge gas flows from the
plenum and over the edge of the substrate to prevent deposition at
the substrate's edge.
Typically, the channel 290 is formed in the upper plate 208.
Optionally, a portion or all of channel 290 may be disposed
completely in the lower plate 210. Optionally, some or all of the
channel 290 may be disposed at least partially in the upper plate
208 and at least partially in the lower plate 210 or various
combinations thereof. Common to these embodiments is that the
mating of the surfaces of the upper and lower plates 208, 210
defines the channels 290 and confines travel of fluids thereto.
FIG. 3A depicts one embodiment of the second surface 232A of the
upper plate 208. In one embodiment, the second surface 232A
includes a plurality of channels 290 formed therein. The channels
290 are configured to fluidly couple a plurality of outlets 304 to
a central origin 306. A fluid source (not shown) supplies a fluid
(e.g., purge gas) through the channels 290 from the central origin
306 to the outlets 304. As it is preferable to maintain
substantially the same pressures at each outlet 304 when the
outlets are spaced equidistantly about the perimeter of the second
surface 232A, the geometry (i.e., cross sectional area) is tuned
for each "leg" of the channels 290 to achieve this goal. As one
skilled in the art will appreciate, the cross section of each leg
of the channel 290 will depend on the desired pressure at the
outlets 304 downstream of the leg and the flow losses encountered
therebetween. The flow losses include such factors such as the
surface roughness and geometry of the leg, number of outlets 304
downstream of the leg, the length of each downstream leg, the flow
properties of the fluid and the like.
In the exemplary embodiment, the channels 290 include a
chevron-shaped primary channel 308 positioned offset from the
center of the upper plate 208. The origin 306 is positioned at the
mid-point of the chevron. Each end of the primary channel 308
branches into a first secondary channel 310, a second secondary
channel 312 and a third secondary channel 314. The secondary
channels 310, 312 and 314 couple the primary channel 308 to the
outlets 304. The first secondary channel 310 and the secondary
channel 312 are co-linearly orientated and have identical cross
sections. The third secondary channel 314 is orientated
substantially perpendicular to the first and second secondary
channels 310, 312. As the third secondary channel 314 is shorter in
length than the first and second secondary channels 310, 312, the
cross sectional area of the third secondary channel 314 is less
than that of the first and second secondary channels 310, 312 to
balance the flow of purge gas passing through the outlets 304.
Optionally, flow restrictors may be placed in the outlets 304 or
elsewhere in the channel to balance the flow.
Alternatively, the outlets 304 may be positioned at varying
distances about the second surface 232A. In such an orientation,
the flow of purge gas from the outlets 304 is desired to be
non-uniform as to balance the flow of purge gas at the substrate's
edge described further below. The flow of gas may be balanced by
controlling the cross sections and lengths of the various channels
as desired to tune the gas flow for the particular application.
FIG. 3B depicts another embodiment of a second surface 232B of the
upper plate 208. Channels 328 are formed in the second surface 232B
of the upper plate 208 to distribute purge gas from a central
origin 320 to a plurality of outlets 322. In one embodiment, four
outlets 322 are disposed equidistant about the perimeter of the
second surface 232B. The outlets 322 that are closest to the
central origin 320 have passages 324 disposed between the central
origin and the respective outlets to provide a conduit for the
purge gas. The outlets 322 that are farthest from the central
origin 320 have passages 326 disposed between the central origin
and the respective outlets to provide a conduit for the purge gas.
To provide a uniform distribution of purge gas to the perimeter of
the second surface 232B, the total flow restriction between the
passages 324, 326 is balanced. Generally, this may be accomplished
by having the cross sectional area of passages 326 greater than the
cross sectional area of passages 324.
FIG. 3C depicts yet another embodiment of a second surface 232C of
the upper plate 208. Channels 342 are formed in the second surface
232C of the upper plate 208 to distribute purge gas from a central
origin 330 to a plurality of outlets. In one embodiment, three
outlets 332, 334 and 336 are disposed at varying distances about
the perimeter of the second surface 232B. The outlet 332 that is
closest to the central origin 330 has a passage 338 disposed
between the central origin and the outlet to provide a conduit for
the purge gas. The outlets 334 and 336 that are farthest from the
central origin 320 have passages 340 disposed between the central
origin and the respective outlets to provide a conduit for the
purge gas. To provide a uniform distribution of purge gas around
the substrate, the flow of purge gas through the outlet 322 must be
greater than the flow through either of the outlets 334 and 336 to
balance the purge gas flowing to the perimeter of the substrate.
Generally, this may be accomplished by having the cross sectional
area of passage 338 greater than the cross sectional area of
passages 340.
Returning to FIG. 2A, the lower plate 210 is fabricated from
ceramic, such as aluminum nitride. Preferably, about 95 percent
pure aluminum nitride is used to enhance the thermal conductivity
of the lower plate 210. The lower plate 210 includes at least one
heating element, such as an embedded electrode 234, having a first
lead 236 and a second lead 238 extending out the second side 214 of
the lower plate 210. The leads 236, 238 are coupled to a power
source (not shown). The power source supplies power to the
electrode 234 to enable the support 202 to heat the substrate 140
to a temperature up to about 300-550 degrees Celsius.
The lower plate 210 additionally includes a vacuum passage 240, a
purge passage 242 and a plurality of lift pin passages 244
extending therethrough. The lift pin passages 244 are generally
disposed radially outwards from the vacuum passage 240 and the
purge passage 242. The lift pin passages 244 extend from the lower
plate 210 through upper plate 208, exiting the upper plate 208
through a tab 219 extending inwards and coplanar to the seal ring
218. (See FIG. 2B). The vacuum passage 240 and the purge passage
242 are generally positioned on opposing sides of the centerline of
the lower plate 210.
The lower plate 210 has a stepped perimeter 260 that extends beyond
the first plate 208. The stepped perimeter 260 supports the shadow
ring 258. The shadow ring 258 generally is annular in form and is
comprised of ceramic such as aluminum nitride. The shadow ring 258
has a first side 270 and a second side 262. The first side 270 is
supported by the perimeter 260. The second side 262 has a lip 264
extending radially inwards. The lip 264 and the lower plate 210
enclose the plenum 266 that receives the purge gas exiting the
outlets 304. The purge gas is disposed about the perimeter of the
substrate 140 through a gap 268 that communicates with the plenum
266 defined between the lip 264 and the upper plate 208. A clip
assembly 272 is utilized to retain the ring 258 to the substrate
support 202. An example of a clip assembly 272 is disclosed by
Yudovsky in previously incorporated U.S. Pat. Ser. No. 09,504,288
(attorney docket No. 4501).
The upper plate 208 and lower plate 210 are fused together. In one
embodiment, the plates 208 and 210 are sintered. To enhance the
integrity of the joint, the plates 208 and 210 should comprise
similar materials (e.g., similar percentage of aluminum nitride) to
minimize differences in thermal expansion. The fusing of the upper
plate 208 and the lower plate 210 makes the channels 290 leak tight
to about 1.times.E-9 sccs helium at 1.times.E-9 Torr
differential.
FIG. 4 depicts the stem 204 in cross section. The stem 204
generally is fabricated from ceramic, such as aluminum nitride.
Typically about 99 percent pure aluminum nitride is preferred to
minimize thermal transfer between the support 202 and stem 204. The
stem 204 is generally tubular in cross section. The stem 204 has an
annular section 402 that defines a central passage 404. A first
projection 406 and a second projection 408 extend from the annular
section 402. The first projection 406 has a purge gas passage 410
and the second projection 408 has a vacuum passage 412 respectively
disposed therethrough. The thickness of the annular section 402 and
the walls of the first and second projections 406, 408 are selected
to minimize thermal conductivity therethrough.
Returning to FIG. 2A, the stem 204 has a first end 246 and a second
end 248. The first end 246 of the stem 204 is connected (e.g.,
fused, bonded or sintered) to the second side 214 of the lower
plate 210. The leads 236, 238 pass through the central passage 404
of the stem 204 and are coupled to a power source (not shown). The
union of the stem 204 and the lower plate 210 places the purge gas
passage 410 disposed in the stem 204 in fluid communication with
the purge gas passage 242 of the lower plate 210 and the channels
290 of the upper plate 208. Purge gas provided from a purge gas
supply (not shown) may be fed through the stem 204 and out the
outlets 304 disposed in the substrate support 202 to minimize
deposition at the substrate's edge. Similarly, the union of the
stem 204 and the lower plate 210 permits the vacuum passage 414
disposed in the stem 204 to be in fluid communication with the
vacuum passage 240 of the lower plate 210 and the vacuum port 250
of the upper plate 208. A vacuum source (not shown) maintains a
vacuum between the substrate 140 and the stepped surface 220 to
retain the substrate 140 during processing by evacuating the volume
between the substrate 140 and stepped surface 220 through the stem
204. The controlled cross section of the stem 204 minimizes the
thermal transfer between the stem 204 and the substrate support
202.
An isolator 254 is disposed at the second end 246 of the stem 204
to minimize the thermal transfer therefrom. The isolator 254 is
typically comprised of a thermally insulative material compatible
with the process environment such as a polymer. In one embodiment,
the isolator 254 comprises a polyimide, for example
VESPELO.RTM..
A heat transfer block 256 couples the stem 204 to the lift system
144. Generally, the heat transfer block 256 is used to remove heat
from the system 100. The fluid temperature can be specified to
control (i.e., increase, maintain, or decrease) the heat transfer
of shaft 204 to heat transfer block 256, to achieve required
thermal uniformity of support 202. The heat transfer block 256 is
generally a thermally conductive material such as aluminum. The
heat transfer block 256 isolates the bellows 146 and lift system
144 from the high temperatures associated with the support assembly
138.
FIG. 5 depicts an exploded view of the second end 248 of the stem
204, the insulator 254 and the heat transfer block 256. The base
248 of the stem 204 includes a plurality of mounting holes 520. A
mounting screw 522, typically comprised of an alloy such as
INCONEL.RTM. or HASTELLOY.RTM., is passed through a clamp ring 524,
the mounting hole 520 in the stem 204 and the insulator 254 and is
threaded into a mating thread hole 526 in the heat transfer block
256. The clamp ring 524 may be separated into more than one part to
facilitate assembly.
The insulator 254 includes a patterned inner diameter 528 that
accommodates the geometry of a seal 508 that is disposed between
the heat transfer block 256 and the stem 204. The seal 508 is
generally annular and comprised of a high temperature elastomer
such as CHEMREZ.TM., KALBEZ.TM., KERREZ.TM., INTERNATIONAL SEAL.
The seal 508 includes two integral tabs 530 extending from a center
ring 534. Each tab 530 has an aperture 532 formed therethrough,
communicating with passages 410 and 412.
The heat transfer block 256 is generally annular in form having an
axially centered passage 536. The heat transfer block 256 has a
first surface 502 that has an outer projection 504 and an inner
projection 506 extending therefrom. The projections 504 and 506 are
configured to house the seal 508 therebetween. Optionally, two
bosses 512 may extend from the first surface 502 between the
projections 504 and 506.
The heat transfer block 256 additionally contains a purge gas
passage 514 and a vacuum passage 516. The passages 514 and 516
extend through the heat transfer block 256 parallel to the
centerline of the heat transfer block 256. The passages 514 and 516
exit the heat transfer block 256 through the bosses 512 and
communicate with the passages 410 and 412, respectively, of the
stem 204. The seal 508 prevents leakage at the junction of the
passages 514 and 410, and passages 516 and 412.
One or more passages 510 are disposed within the heat transfer
block 256. The passages 510 are coupled to a fluid source (not
shown). Heat transfer fluid, such as de-ionized water, is passed
through the passages 510 to regulate the temperature of the heat
transfer block 256. The seal 508, being substantially enclosed by
the projections 514 and 516 and the bosses 512 of the heat transfer
block 256, is generally protected from heat propagated through the
stem 204 from the substrate support 202 by controlling the
temperature of the heat transfer block 256.
In operation, the semiconductor substrate 140 depicted in FIG. 1 is
secured to the support assembly 138 by providing a vacuum
therebetween. The expanded portion 252 of the vacuum port 250
minimizes the local pressure drop and corresponding temperature
change of gases being drawn into the vacuum port 250, thus
preventing localized cooling on portion of the substrate directly
above the vacuum port 250.
The temperature of the substrate 140 is elevated to a predetermined
process temperature primarily providing power to the electrode 234.
The stepped surface 220 provides a variable gap that counters the
tendency of the substrate 140 to have a higher temperature at the
center of the substrate 140. During the deposition process, the
substrate 140 is heated to a steady state temperature. Using
thermal control of both the lid 110 and the support assembly 138,
the substrate 140 is maintained at a temperature of 300-550 degrees
Celsius
Gaseous components, which in one embodiment may include silane and
tungsten hexafluoride, are supplied from a gas panel to the process
chamber through mixing block 134 and showerhead 118 to form a
gaseous mixture. The gaseous mixture reacts to form a layer of
tungsten on the substrate 140. To prevent deposition at the
substrate's edge and possible adherence of substrate 140 to the
support assembly 138, purge gas is flowed into the plenum 266 from
the channels 290, and distributed through the gap 268 between the
shadow ring 258 and the support 202 to the perimeter of the
substrate 140.
Although the teachings of the present invention that have been
shown and described in detail herein, those skilled in the art can
readily devise other varied embodiments that still incorporate the
teachings and do not depart from the scope and spirit of the
invention.
* * * * *